As is well known, a large number of computers are now available for handling input information or data and of course are capable of handling such data extremely rapidly. As a practical matter, many of the computers now are not fully utilized, and so little in some cases that their installations are barely economically justifiable.
The main reason for minimal usage is the expense of existent computer terminals which is such that their wide general use is economically prohibitive. For example, the total cost of 30 computer terminals for educational purposes in a classroom currently far exceeds the cost of the computer itself. To a large extent this excessive cost is due to the expense of the printing mechanism, it being generally accepted that printed input and output data are a practical necessity. Conventional impact printing such as is performed by electric or manual typewriters obviously requires a relatively expensive mechanism and is high in its operating energy requirements. Electrostatic varieties of printing require high voltages, and thermal techniques employing a heat-sensitive paper utilize thermal heads with transistors having a relatively high thermal mass so as to require considerable amounts of energy to heat up the necessary printing temperature of approximately 170.degree. Centigrade, and at the same time having high thermal inertia which limits the printing speed. Fabrication of such a head is currently expensive as well.
Further reasons for minimal usage are: the terminals have to be connected directly by special lines or indirectly via the phone line to the computer. In the former case, accessibility to the computer is limited to permanent installations close to the computer, while in the latter case, the bandwidth of the phone line limits the printing speed to 30 characters/sec. and requires the telephonic link, and with current models the mains (115 volts AC), to be also present.